This exploratory R21 grant application is intended to establish research paradigms for, and make preliminary progress toward, understanding the neural bases of individual differences in the personality trait of impulsivity. Given the demonstrated relation between impulsive personality and negative health behavior, including drug use, a better understanding of this personality trait would be of considerable public health value. Relatively little is known about how normal personality is reflected in the brain. Most of what we do know relates to neurochemistry, as opposed to the more "molar" systems level typical of cognitive neuroscience. As such, the overall goal of this application is to relate normal variation in impulsivity to variation in brain function at this "molar" level of description, that is, in terms of large-scale networks of functionally delineated brain regions. Preliminary work by the principal investigator suggests that systematic relationships can be found between personality impulsivity and brain function at this level of analysis. Normal subjects' performance on a battery of behavioral tasks showed a strong association between a common measure of impulsivity and the functions of prefrontal cortex (PFC). The specific aims of this research are: (1) to go beyond global descriptions of PFC function, to discover which subsystem(s) of PFC are related to personality differences in impulsivity; (2) to go beyond a single conception of impulsivity, to consider the neural bases of several other well-known (and uncorrelated) measures of impulsivity; (3) to gather both hypothesis-driven and exploratory functional MRI data, for purposes of testing hypotheses generated from Aims 1 and 2, concerning the differences in brain function that underlie the normal personality trait of impulsivity, and for exploring the various ways in which differences in brain activation could relate to impulsivity.